Grain crops are grown for a variety of purposes, such as in feed, food and industrial applications. In producing and using grain, it is common that the different components of the grain need to be separated for optimum use in an industry. In crops in which the grain has a seed coat or pericarp, separation of the pericarp from the other seed components, the endosperm and embryo (germ), is desirable.
For example, one such application is in the separation of these seed components in the use of crop grain to produce ethanol. The replacement of fossil fuel as an energy source has led to interest in identifying renewable energy sources. One such source is the use of crop plants to produce ethanol. An example of one such crop plant is corn, used to produce ethanol, typically using either wet milling or dry grinding processes. In wet milling, corn is steeped in a liquid mixture including sulfur dioxide for a period of between 24 and 36 hours to soften the materials and loosen the components of the kernel. The corn and liquid is put in a mill that grinds the corn to free the germ from the kernel. The germ floats to the top of the slurry and can be separated. The starch, protein and fiber that remain are separated to produce pure starch. The starch is cooked and fermented, and finally distilled to produce ethanol. In dry grind ethanol production, corn is ground, mixed with water, cooked, fermented and distilled.
An important aspect of increasing the feasibility of ethanol production is to optimize use of the by-products produced in this process. High raw material and costs of bringing the raw material to plants, the cost of enzymes, yeast and chemicals used in the process, and capital and labor costs are limitations on economics of ethanol production. In the dry-grind process, no distinction is made between the fermentable starch and non-fermentable components of the seed, namely the germ, fiber and protein. These components are recovered together as a single entity, and are termed distillers dried grains with solubles, also known as DDGS. There is keen interest in the separation of these components from each other, and improvement in purity, in order that they may be sold for separate uses and improve the economics of the operation. The ability to market and sell DDGS is a limiting factor in the growth and expansion of dry-grind ethanol production facilities. Conventional wet milling provides an alternative to produce value-added products from corn, however, this process requires a large capital investment and focuses on producing clean starch for further processing into modified starches, corn syrup, high fructose corn syrup and other products.
With the increase in ethanol production from dry-grind facilities, DDGS production has doubled to 7 MM metric tons from 2000 to 2005. During this time period, the average market value of DDGS has declined from approximately $115/ton to $65/ton. This represents an annual decrease of 10% per year. The demand for renewable energy sources will continue to offset the limited availability of fossil fuels. With the continued expansion of ethanol to meet demand for energy, the trend in declining DDGS prices will likely continue.
Previous attempts have been made to separate fiber from endosperm and germ. One example is found at Singh et al., U.S. Pat. No. 6,254,914, in which a two-step process is used where specific gravity of a slurry including germ and fiber is maintained at 7.5 to 11 Baumé to remove germ, and in the second step, fiber removed by increasing the specific gravity to 11 to 16 Baumé. In an alternative, fiber and germ are removed by subjecting the slurry to a Baumé of 11 to 16.
Thus there is a need to improve recovery and purity of these components of the seed.